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United States Patent |
6,079,819
|
Deshpande
,   et al.
|
June 27, 2000
|
Ink jet printhead having a low cross talk ink channel structure
Abstract
An ink jet printhead is disclosed which has a heater plate containing the
heating elements and driving circuitry means monolithographically formed
on one surface thereof and the ink flow directing channel structure is
formed on the heater plate using a layer of patternable polymeric material
which, in one embodiment, is exposed using a mask to define the channel
pattern then developed and cured. After curing, the patterned channel
structure is polished to provide a smooth coplanar surface and a cover
plate with an aperture therein is aligned and bonded to the channel
structure to complete the printhead. The aperture serves as both ink inlet
and a portion of the ink reservoir. The channels are open at one end and
serve as the droplet ejecting nozzles, while the other ends are closed and
extend beneath the cover plate aperture to provide a baffled portion of
the ink reservoir and prevent cross-talk between the ink channels. In
another embodiment, the channels ends opposite the nozzles open into a
common recess with the channels walls extending therein to function as
baffles and prevent cross-talk.
Inventors:
|
Deshpande; Narayan V. (Penfield, NY);
Andrews; John R. (Fairport, NY);
Ims; Dale R. (Webster, NY)
|
Assignee:
|
Xerox Corporation (Stamford, CT)
|
Appl. No.:
|
004640 |
Filed:
|
January 8, 1998 |
Current U.S. Class: |
347/65; 347/63 |
Intern'l Class: |
B41J 002/05 |
Field of Search: |
347/54,56,61,63,65
|
References Cited
U.S. Patent Documents
Re32572 | Jan., 1988 | Hawkins et al. | 156/626.
|
4774530 | Sep., 1988 | Hawkins.
| |
4835553 | May., 1989 | Torpey et al.
| |
4947192 | Aug., 1990 | Hawkins et al.
| |
4947193 | Aug., 1990 | Deshpande.
| |
5132707 | Jul., 1992 | O'Neill.
| |
5198834 | Mar., 1993 | Childers et al.
| |
5385635 | Jan., 1995 | O'Neill | 347/65.
|
5665249 | Sep., 1997 | Burke et al.
| |
5686224 | Nov., 1997 | O'Neill.
| |
5699094 | Dec., 1997 | Burke et al. | 347/63.
|
5708465 | Jan., 1998 | Morita et al. | 347/65.
|
5760803 | Jun., 1998 | Yamamoto et al. | 347/65.
|
5870123 | Feb., 1999 | Lorenze, Jr. et al. | 347/65.
|
5912685 | Jun., 1999 | Ramon | 347/65.
|
Primary Examiner: Brase; Sandra
Attorney, Agent or Firm: Chittum; Robert A.
Claims
We claim:
1. An ink jet printhead having a patternable ink channel structure which
minimizes cross-talk, comprising:
a heater plate having on one surface thereof an array of heating elements,
driving circuitry means, and interconnecting leads including contacts for
the selective application of electrical pulses to each of the heating
elements, each of the selectively applied pulses ejecting an ink droplet
from the printhead;
a passivation layer covering the heater plate surface and the driving
circuitry means and interconnecting leads thereon, the heating elements
and contacts being free of the passivation layer;
a patternable layer being deposited on the passivation layer and patterned
to expose the contacts and to form a common recess and a plurality of
parallel channel grooves therein with opposing ends, each channel groove
containing and exposing therein a heating element, one end of the channel
grooves being open and the opposing end being connected to the common
recess; and
a cover plate having an aperture, the cover plate being aligned and bonded
to the patternable layer to form ink channels from the channel grooves and
nozzles from the channel open ends, the aperture being aligned over at
least a portion of the common recess and a portion of the ends of the
channel grooves which are connected to the common recess, so that the
aperture and common recess form an ink reservoir for the printhead and the
aperture provides an ink inlet to said reservoir while the channel end
connected to the common recess extend into said ink reservoir and function
as baffles to prevent cross-talk between channels when the printhead is
printing.
2. The printhead as claimed in claim 1, wherein the patternable layer is a
photopatternable polymeric material.
3. The printhead as claimed in claim 2, wherein the walls of the channel
grooves extend into the reservoir for a distance `O` of at least 25 .mu.m.
4. The printhead as claimed in claim 3, wherein the cover plate may be
fabricated from either glass, quartz, silicon, polymeric, or ceramic
material.
5. The printhead as claimed in claim 1, wherein each of the channel ends
which extend into the reservoir alternately extend a varying distance into
said reservoir.
6. The printhead as claimed in claim 5, Wherein one of said alternately
extending channel ends extends into the reservoir for a distance of at
least 25 .mu.m and an adjacent channel end extends a great distance into
the reservoir.
7. An ink jet printhead having a patternable ink channel structure which
minimizes cross-talk, comprising:
a heater plate having on one surface thereof an array of heating elements,
driving circuitry means, and interconnecting leads including contacts for
the selective application of electrical pulses to each of the heating
elements, each of the selectively applied pulses ejecting an ink droplet
from the printhead;
a passivation layer covering the heater plate surface and the driving
circuitry means and interconnecting leads thereon, the heating elements
and contacts being free of the passivation layer;
a patternable layer being deposited on the passivation layer and patterned
to expose the contacts and to form a plurality of parallel channel grooves
and a reservoir groove therein, the channel grooves each having a heating
element therein, each channel groove having an open end and an opposite
end which connects to the reservoir;
a cover plate having an aperture, the cover plate being aligned and bonded
to the patternable layer to form ink channels from the channel grooves,
nozzles from the channel groove open ends, and ink reservoir for the
printhead from the combination of the reservoir groove, channel ends which
connect to the reservoir groove, and aperture, the aperture providing the
inlet to the printhead reservoir; and
the channel ends connecting to the reservoir groove having walls which
extend into the printhead reservoir a predetermined distance and provide
baffling of back flow from channel which eject ink droplets and to prevent
crosstalk.
8. The printhead as claimed in claim 7, wherein each of the channel walls
alternately extend into the printhead reservoir by varying distances.
9. The printhead as claimed in claim 8, wherein one of said channel wall
extends into the printhead reservoir for a distance of at least 25 .mu.m
and adjacent channel wall extends a greater distance into the printhead
reservoir.
10. The printhead as claimed in claim 7, wherein the predetermined distance
that the channel groove walls extend into the printhead reservoir is at
least 25 .mu.m.
11. The printhead as claimed in claim 7, wherein the cover plate may be
fabricated from either glass, quartz, silicon, polymeric, or ceramic
material.
12. The printhead as claimed in claim 7, wherein the patternable layer is a
photopatternable polymeric material.
Description
BACKGROUND OF THE INVENTION
This invention relates to ink jet printing devices and more particularly to
thermal ink jet printheads having a patternable ink flow directing channel
structure with a geometry to minimize crosstalk.
In one conventional thermal ink jet printhead, the printhead consists of
two sections, a heater plate and a channel plate. Some geometrical
features are formed in both plates in such a way that, when bonded
together, they form the desired configuration for ink droplet ejection.
For example, U.S. Pat. No. 4,774,530 discloses a printhead in which upper
and lower silicon substrates are mated and bonded together with a thick
film insulative layer sandwiched therebetween. One surface of the upper
substrate or channel plate has a plurality of parallel grooves and a
recess etched therein. When mated with the lower substrate or heater
plate, the grooves and recess form the printhead ink channels and ink
reservoir, respectively. The grooves are open at one end and closed at the
other end. The channel open ends serve as the printhead nozzles. The
channel closed ends are closely adjacent the reservoir and placed in fluid
communication therewith by a patterned recess in the thick film layer.
Each channel is capillarily filled with ink from the reservoir and has a
heating element located upstream of the nozzles. Each heating element is
selectively addressable by electrical pulses representative of data
signals to produce momentary vapor bubbles in the ink to effect the
ejection of ink droplets from the printhead nozzles and propel them to a
recording medium. The thick film layer is also patterned to expose the
heating elements and thereby place the heating elements in a pit to better
contain the vapor bubble and prevent ingestion of air.
This printhead construction has some drawbacks. For example, the silicon
channel plate is anisotropically or orientation dependent etched to form
straight, triangularly shaped grooves when non-straight grooves provide
more design flexibility and non-triangular shaped nozzles assist in
droplet directionality. In addition, an etched silicon channel plate means
separate fabrication of the two plates and the necessity of very accurate
alignment between the two when they are mated. Because silicon is opaque,
it is difficult to determine if the adhesive is coating all of the surface
areas required to separate the channels and to prevent internal ink leaks.
U.S. Pat. No. 5,132,707 discloses a thermal ink jet printhead having an
array of coplanar nozzles in a nozzle face that are entirely surrounded by
a polymeric material. The ink channels, nozzles, and ink reservoir are
produced by sequentially depositing and patterning two layers of polymeric
material, such as, for example, Vacrel.RTM., on the heater plate, so that
the heating elements are placed in a pit in the first layer and the
channels and reservoir recesses are produced in the overlying second
layer. The cover plate has a third layer of identical polymeric material
with a hole through both the cover plate and third layer to serve as the
ink inlet. The cover plate with the third layer is aligned and bonded to
the second layer with the cover plate hole aligned with the reservoir
recess in the second layer to produce the printhead.
U.S. Pat. No. 5,198,834 discloses a printhead or pen head for a
droplet-on-demand ink jet printer or pen which utilizes a barrier wall
located between a substrate and an orifice plate. The ink flows through
the printhead in channels defined in the barrier wall. The barrier wall is
fabricated in two layers from cured, photoimaged resist materials. One
layer is a soldermask material, and the other is a photolithographic
resist material. The two layers together resist chemical attack by the ink
and separation of the orifice plate from the printhead.
Pending U.S. Patent Application Ser. No. 08/712,761, filed Sep. 12, 1996,
entitled "Method and Materials For Fabricating An Ink Jet Printhead," and
assigned to the same assignee as the present invention discloses an ink
jet fabrication technique which enables capillary channels for liquid ink
to be formed with square or rectangular cross-sections. A sacrificial
layer is placed over the main surface of a silicon chip, the sacrificial
layer being patterned in the form of the void formed by the desired ink
channels. A permanent layer comprising a permanent material is applied
over the sacrificial layer and, after polishing the two layers to form a
uniform layer which exposes some of the surfaces of the sacrificial layer,
the sacrificial layer is removed to form open ink channels. A cover plate
is bonded to the patterned permanent material to provide the closed ink
channels and produce the printhead. Preferred sacrificial layer materials
include polyimide while the preferred permanent layer materials include
polyarylene ether.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an ink jet printhead having an
ink channel structure which is formed directly on the heater plate,
wherein said channel structure minimizes fluidic crosstalk between
neighboring channels.
In one aspect of the present invention, there is provided an ink jet
printhead having a low cross talk channel structure, comprising: a heater
plate having on one surface thereof an array of heating elements, driving
circuitry means, and interconnecting leads including contacts for the
selective application of electrical pulses to each of the heating
elements, each of the selectively applied pulses ejecting an ink droplet
from the printhead; a passivation layer covering the heater plate surface
and the driving circuitry means and interconnecting leads thereon, the
heating elements and contacts being free of the passivation layer; a
patternable polymer layer being deposited on the passivation layer and
patterned to expose the contacts and to form a plurality of parallel
channel grooves therein with opposing ends, each channel groove containing
and exposing therein a heating element, one end of the channel grooves
being open and each of the opposing ends being closed; and a cover plate
having an aperture and being bonded to the patternable polymer layer to
form the ink channels from the channel grooves and nozzles from the
channel open ends, the aperture being aligned with the closed ends of the
channel grooves to provide both an ink inlet and an ink reservoir.
In one embodiment of the invention, the cover plate aperture has a size
sufficient to expose the closed end portions of the channel grooves in
such a manner that the walls between channel grooves in the vicinity of
the closed ends thereof extend into the space functioning as the ink
reservoir and provide a geometry which eliminates crosstalk between the
ink channels ejecting droplets and the adjacent ink channels that are not
ejecting droplets.
In another embodiment, the channel groove ends opposite the open ends
connect to a common recess which will subsequently serve as a portion of
the printhead reservoir. In a further embodiment the ends of the channel
grooves which connect to the common recess have walls which extend into
the common recess by varying distances.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described by way of example with
reference to the accompanying drawings, wherein like reference numerals
refer to like elements and in which:
FIG. 1 is a schematic isometric view of a printhead in accordance with the
present invention and oriented so that the droplet ejecting nozzles are
shown;
FIG. 2 is a cross-sectional view of FIG. 1 as viewed along the view line
2--2 thereof;
FIG. 3 is a schematic isometric view of the printhead of FIG. 1 without the
cover plate;
FIG. 4 is a view similar to that of FIG. 2 showing the dimensional spacing
between portions of the ink channel;
FIG. 5 is a view similar to FIG. 2 showing an alternate embodiment of the
printhead cover plate;
FIG. 6 is a view similar to FIG. 3 showing an alternate embodiment wherein
the channel grooves open into a common recess with the walls of the
channel grooves extending into the printhead reservoir;
FIG. 7 is a partially shown plan view of an alternate embodiment of the
printhead without the cover plate showing the channel groove walls
extending into the reservoir by varying distances; and
FIG. 8 is a cross-sectional view similar to FIG. 2 showing another
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, a schematic isometric view of an ink jet printhead 10 in
accordance with the present invention is shown mounted on a heat sink 26
and oriented to show the front face 29 of printhead and the array of
droplet ejecting nozzles 27 therein. Referring also to FIG. 2, a
cross-sectional view of FIG. 1 taken along view line 2--2 through one ink
channel 20, the silicon heater plate 28 has the heating elements 34,
driving circuitry means 32 represented by dashed line, and leads 33
interconnecting the heating elements and driving circuitry means and
having contacts 31 connected to a printed circuit board 30 by wire bonds
25. The circuit board is connected to a controller or microprocessor of
the printer (neither shown) for selectively applying a current pulse to
the heating elements to eject ink droplets from the nozzles. One suitable
driving circuitry means is described in U.S. Pat. No. 4,947,192 and is
hereby incorporated by reference. Generally, an underglaze layer 14 is
formed on the heater plate surface on which the heating elements, driving
circuitry means, and leads are to be formed, followed by a passivation
layer 16 which is patterned to expose the heating elements and contacts.
Although the preferred embodiment has a photosensitive polymer layer, any
patternable material which is not attacked by the ink would be sufficient,
and any wet or dry etching process could be used to pattern the
patternable material, including reaction ion etching (RIE) or
photolithography. A photosensitive polymeric material is deposited over
the heater plate to form the photopolymer layer 24 and
photolithographically patterned to produce the ink channels 20 having an
open end to serve as a nozzle 27 and a closed end 21 and to expose the
contacts 31 of the electrical leads. A cover plate 22 of glass, quartz,
silicon, polymeric, or ceramic material has an aperture 23 therethrough,
and is bonded to the surface of the patterned photopolymer layer 24 with a
suitable adhesive (not shown). The cover plate aperture 23 has a size
suitable to expose portions of the closed ends 21 of the channels and to
provide an adequate ink supply reservoir for the printhead, when combined
with closed end portions 21 of the channels. The ink flow path from the
reservoir to the channels 20 is indicated by arrow 19. An optional nozzle
plate 12 is shown in dashed line which is adhered to the printhead front
face 29 with the nozzles 13 therein aligned with the open ends 27 of the
channels 20 in the photopolymer layer 24.
As disclosed in U.S. Pat. Nos. Re. 32,572, 4,774,530, and 4,947,192 all of
which are incorporated herein by reference, the heater plates of the
present invention are batch produced on a silicon wafer (not shown) and
later separated into individual heater plates 28 as one piece of the
printhead 10. As disclosed in these patents, a plurality of sets of
heating elements 34, driving circuitry means 32, and electrical leads 33
are patterned on a polished surface of a (100) silicon wafer which has
first been coated with an underglaze layer 14, such as silicon dioxide
having a thickness of about 1-5 .mu.m. The heating elements may be any
well known resistive material such as zirconium boride, but is preferably
doped polycrystalline silicon deposited, for example, by chemical vapor
deposition (CVD) and concurrently monolithically fabricated with the
driving circuitry means as disclosed in U.S. Pat. No. 4,947,193.
Afterwards, the wafer is cleaned and re-oxidized to form a silicon dioxide
layer (not shown) over the wafer including the driving circuitry means. A
phosphorous doped glass layer or boron and phosphorous doped glass layer
(not shown) is then deposited on the thermally grown silicon dioxide layer
and is reflowed at high temperatures to planarize the surface. As is well
known, photoresist is applied and patterned to form vias for electrical
connections with the heating elements and driving circuitry means and
aluminum metallization is applied to form the electrical leads and provide
the contacts for wire bonding to the printed circuit board which in turn
is connected to the printer controller. Any suitable electrically
insulative passivation layer 16, such as, for example, polyimide,
polyarylene ether ketone, polybenzoxazole, or bisbenzocyclobutene (BCB),
is deposited over the electrical leads to a thickness of about 0.5 to 20
.mu.m and removed from the heating elements and contacts.
Next, an optional pit layer 36 of, for example, polyimide or BCB, may be
deposited and patterned to provide pits 38 for the heating elements as
shown in FIG. 8 and disclosed in U.S. Pat. No. 4,774,530. The optional pit
layer 36 is deposited and patterned prior to the deposition of the
photopolymer layer 24. However, for high resolution printheads having
nozzles spaced for printing at 400 spots per inch (spi) or more, heating
element pits have been found not to be necessary, for the vapor bubbles
generated to eject ink droplets from nozzles and channels of this size
tend not to ingest air.
If the topography of the heater wafer is uneven, the wafer is polished by
techniques well known in the industry, such as that disclosed in U.S. Pat.
No. 5,665,249 and incorporated herein by reference. Then the
photopattemable polymer layer which is to provide the channel structure 24
is deposited. As disclosed in U.S. application Ser. No. 08/712,761 filed
Sep. 12, 1996, mentioned above, and incorporated herein by reference, a
suitable channel structure material must be resistant to ink, exhibit
temperature stability, be relatively rigid, and be readily diceable. The
most versatile material for a channel structure is polyimide or
polyarylene ether ketone (PAEK). In the preferred embodiment, OCG 7520.TM.
polyimide is used, and because polyimide shrinks about 30 to 50% when
cured, this must be taken into account when depositing a layer of
polyimide on the heating element wafer. After deposition of the polyimide,
it is exposed using a mask with the channel sets pattern and contacts
pattern. The patterned polyimide channel structure layer is developed and
cured. In one embodiment, the channel structure thickness is 30 .mu.m, so
the original thickness deposited is about 65 .mu.m, which shrinks to about
33 .mu.m when cured and is then polished to the desired 30 .mu.m by the
same technique used to polish the surface of the heater wafer mentioned
above. For the embodiment having a channel structure thickness of 16
.mu.m, the original thickness deposited must be about 40 .mu.m, which
shrinks to about 20 .mu.m when cured and is then polished to the desired
16 .mu.m thickness. After the patterned polyimide layer 24 is cured and
polished, a cover plate 22, the same size as the wafer and having a
plurality of apertures 23 therein, is bonded to the polyimide layer. The
cover plate 22 serves as the closure for the channels 20 and the cover
plate aperture 23, which is an opening through the cover plate, serves as
an ink inlet to the reservoir as well as most of the ink reservoir. The
silicon wafer and wafer size cover plate with the channel structure
sandwiched therebetween are separated into a plurality of individual
printheads by a dicing operation. The dicing operation not only separates
the printheads, but also produces the printhead front face 29 and opens
one end of the channels to form the nozzles 27.
Referring to FIG. 3, a schematic isometric view of a portion of the heater
wafer is shown, comprising a single heater plate 28 having the patterned,
cured, and polished polyimide channel structure 24 thereon. The cover
plate is omitted, but the aperture 23 therein is shown in dashed line, so
that the position of the ink inlet and reservoir provided by the aperture
relative to the channel closed ends 21 is identified. This geometry of the
closed end portions of the channels and cover plate aperture defines the
ink reservoir as including the closed end portions of the channels. Thus,
the portion of the channel walls 45 which extend into the reservoir act as
a baffle when a heating element is addressed with an electrical pulse to
form an ink vapor bubble which concurrently causes the ejection of an ink
droplet and a back pressure towards the reservoir. The back pressure
produces a flow of ink into the reservoir with the baffling walls of the
channels causing the ink to flow upward and away from the neighboring
channels. Since the reservoir portion comprising the relatively large
cover plate aperture provides much less flow resistance than that of the
portion comprising the closed end portions of the neighboring channels,
the primary back flow path is, therefore, into the aperture portion of the
reservoir and not into the neighboring channels. Without the channel walls
to baffle the ink back flow, the ink at the nozzles of the adjacent
non-addressed or non-fired channels would bulge out significantly and weep
onto and wet the front face 29 of the printhead in the regions surrounding
the nozzles 27. Thus, the adjacent or nearest nozzle to the nozzle
ejecting a droplet tends to flood ink onto the front face, while an
unfired or non-ejecting nozzle which is sandwiched between two nozzles
which are ejecting droplets may also cause the ejection of an ink droplet.
This affect on the adjacent or near non-fired channels by the fired
channels is termed "cross-talk."
FIG. 4 is similar to FIG. 2, with the various channel portions identified.
For the preferred embodiment of a 600 spi printhead, the cover plate has a
thickness of about 25 to 500 .mu.m and the aperture is an elongated slot
having a length sufficient to extend across all of the channels and has a
width `W` of 100 to 1000 .mu.m. The thickness `T` of the channel structure
24 is about 16-30 .mu.m and the channel width is about 30 .mu.m, so that
in one embodiment, the channel cross-section is about 30 .mu.m.times.30
.mu.m. The frequency response is controlled by the rear channel length `R`
which is about 50 .mu.m. The rear end portion `O` of the channels or the
portion of the closed end portion which extends into and becomes a part of
the reservoir affects the refill of the channels, if they are too small,
but for sufficiently large openings that parameter has no effect on
droplet ejection or refill. A sufficient dimension for the rear end
portion `O` is equal to or greater than 25 .mu.m. The required refill
parameters and the control of cross-talk can be achieved by adjusting the
dimensions R, O, and T. The heating element is about 50-100 .mu.m long
(`H`) and about 25 .mu.m wide. The heating element is spaced upstream from
the nozzle or front face by the dimension `F` of about 40-90 .mu.m, but
preferably 50 .mu.m. The optional nozzle plate 12 shown in dashed line is
about 50 .mu.m thick and has a conical shaped nozzle 13 for each nozzle 27
in the printhead front face. The conical shaped nozzle is aligned and has
its axis 42 substantially coincident with the axis 40 of the channels. The
outside opening of the nozzle 13 is about 17 .mu.m in diameter and the
inside opening adjacent the nozzle 27 is about 26 .mu.m in diameter.
FIG. 5 is a view similar to FIG. 2, but showing an alternate embodiment of
the cover plate. In this embodiment, a silicon substrate is utilized for
the cover plate 22' and has an aperture 23' formed by orientation
dependent etching (ODE). The etching is done from the silicon cover plate
surface which is to be bonded against the channel structure 24, thereby
providing a different cross-sectional shape for the reservoir.
Referring to FIG. 6, another embodiment is shown of the channel structure
24 in a view similar to that of FIG. 3. In this embodiment, the channel
ends 21' connect and open into a common recess 41. Because walls 45 of the
channels 20 extend into the reservoir formed by combination of the cover
plate aperture 23, common recess 42, and end portions of the channels ends
21' by the distance `O` of at least 25 .mu.m, cross-talk is prevented.
FIG. 7 is an alternate embodiment of the channel structure 24 in FIG. 6. In
this embodiment of a printhead, a partially shown plan view of the channel
structure 24 is depicted showing that the channel walls 45 of the channels
ends 21' vary in the distance in which they extend into the reservoir
portion formed by the cover plate aperture 23 as represented by `O` and
O', where O is at least 25 .mu.m and O' is greater than O. Any combination
of varying channel wall extensions into the reservoir may be used, such
as, the walls of the outer channels of particular groups of channels (not
shown) may extend further into the reservoir than the intervening channel
walls.
FIG. 8 is a cross-sectional view similar to that of FIG. 2, but has a pit
layer 36 taught by U.S. Pat. No. 4,774,530. The pit layer 36 may be useful
for printheads having a resolution of less than 400 spi, but may be used
for higher printing resolution printheads. Except for the pit layer, the
printhead and method of fabrication is same as for the printhead in FIGS.
1 and 2.
Although the foregoing description illustrates the preferred embodiment,
other variations are possible and all such variations as will be apparent
to those skilled in the art are intended to be included within the scope
of this invention as defined by the following claims.
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